This invention relates to a heat exchanger for transferring heat between two gas-flow paths, and more particularly concerned with a substantially counterflow isolating heat exchanger having separate primary and secondary gas flow circuits between which there are good heat transfer properties. The invention is particularly suitable for use in air-conditioning and ventilation systems.
Air flow isolating heat exchangers are becoming increasingly important to reduce the cost of heating or cooling of an outdoor air supply fed into an enclosed space such as a building. Such heat exchangers are required to handle air flows for small and large spaces from 50 1/s to 10,000 1/s of outdoor air, ideally transferring the sensible and latent heat from the stale exhaust air of the room.
The conventional form of heat exchanger for use with gases is the parallel plate heat exchanger. This comprises a stack of spaced parallel thermal conductive plates, which define between them, pockets through which the gas flows. Alternate pockets are connected to carry one of the two gas streams between which heat is to be transferred, and the remaining pockets carry the other gas stream. Gas has a lower heat content than liquid. This has led to the development of heat exchangers in which the gas-flow paths have a large cross-sectional area, using thin materials which are preferred because the transfer of heat from a gas to a surface along which it is traveling takes place more slowly than is the case with a liquid which wets the surface.
In order to extend the xe2x80x9cdwell timexe2x80x9d of the gases in the heat exchanger, it has been proposed to provide thin, substantially parallel baffles in the pockets which extend the length of the gas flow path through them and are in good thermal contact with the plates. Such an arrangement is disclosed in the U.S. Pat. No. 5,829,513 (Urch). This patent discloses the feature of providing a sinuously wound thermal conductive membrane with a stack of parallel pockets each of which contain a molded plastic skeletal insert. The insert comprises a flat frame supported within it a set of parallel baffles which define a platen of passageways, extending between the inlet and outlet openings which is provided in the frame.
Whilst the heat exchanger disclosed in U.S. Pat. No. 5,829,513 has a number of advantages, it also has a number of disadvantages. Firstly, gas traveling through a particular passageway in the heat exchanger spends a different xe2x80x9cdwell timexe2x80x9d to that of gas passing through an adjacent passageway in the same pocket. Whilst each of the passageways are of substantially the same width, as shown in FIG. 3 of U.S. Pat. No. 5,829,513, they are nested in a U-shape, such that the outer passageways are longer than the inner passageways. This means gas entering an inner passageway travels through it quicker than gas passing through an outer passageway. The xe2x80x9cdwell timexe2x80x9d is the period the gas spends within the passageway. The dwell time for gas passing through an outer, longer passageway is longer than that of the dwell time for gas passing through an inner, shorter passageway. These differences in dwell times affect the overall efficiency of the heat exchanger. Another disadvantage with the heat exchanger disclosed in U.S. Pat. No. 5,829,513 is that it has a high pressure drop and therefore requires substantial fan power to urge gas therethrough.
The present invention provides an improved heat exchanger for transferring heat between two separate gas-flow paths.
In accordance with a first aspect, the present invention consists in a gas-flow heat exchanger comprising a set of parallel, spaced, heat-conductive areas providing between them a stack of pockets each containing parallel baffles which define a platen of passageways guiding the gas-flow path through the pocket between inlet and outlet openings, the openings being arranged in four parallel lines at the sides of the stack, two of the lines respectively containing the inlet and outlet openings associated with the gas-flow paths of alternative pockets of the stack, while the remaining two lines respectively contain the inlet and outlet openings associated with the remaining pockets of the stack of the heat exchanger, each pocket containing a removable frame formed with the openings provided at the ends of the gas flow path through it and supporting within the frame the parallel baffles which divide the gas-flow path into the platen of passageways, characterized in that all of the passageways provide a substantially equal dwell time to gas passing therethrough.
In one embodiment each of the passageways has a substantially equal length. Preferably the baffles define a substantially S or Z- shaped platen of passageways. Preferably the platen of passageways of one of the pockets is the mirror image of the platen of passageways of an adjacent pocket to provide crossover counterflow. Preferably the inlet of each passageway is on an opposite side of the stack to that of its outlet.
In another embodiment each platen of passageways is a nest of substantially U-shaped passageways. The length of one of the U-shaped passageways is greater in length than that of an adjacent U-shaped passageway inwardly nested thereto. Preferably the inlet opening and outlet opening of one of the U-shaped passageways is larger in size to the inlet opening and outlet opening of an adjacent U-shaped passageway inwardly nested thereto. Preferably each successive U-shaped passageway has a larger inlet and outlet opening than a passageway inwardly nested thereto.
Preferably each of the pockets contains an identical structure of frame and baffles, differently oriented so that the opening associated with alternative pockets lie in two lines, and the openings associated with the remaining pockets lie in two different lines. Preferably the parallel heat-conductive areas separating the pockets from one another are formed from spaced rectangular or square areas of a sinuously wound heat conductive material.
Preferably the heat conductive material is selected from the group consisting of a metal foil and thin plastic foil. Preferably the heat conductive material is a moisture permeable material that can transfer both sensible heat and latent heat.
Preferably in one embodiment the moisture permeable material is paper. Preferably the paper has a high water strength texture. Preferably the paper is kraft paper. Preferably the kraft paper weighs about 45 grains per square meter.
Preferably in another embodiment the moisture permeable material is a finely woven plastic material.
Preferably the combination of frame and baffles is provided by a skeletal structure. Preferably the skeletal structure is plastic.
An air conditioning system utilizing a gas-flow heat exchanger in accordance with the first aspect of the invention as abovementioned, wherein an air supply fan is in fluid communication with one of the lines containing inlet openings at the side of the stack to deliver air thereto, and an exhaust fan is in fluid communication with another of the lines containing inlet openings at the side of the stack to deliver exhaust air from the space being air-conditioned.
In one arrangement the supply fan and the exhaust fan are adjacent to each other on the same side of the stack.
In another arrangement the supply fan and the exhaust fan are on opposite sides of the stack.
An air conditioning system utilizing a gas-flow heat exchanger in accordance with the first aspect of the invention as abovementioned, wherein air having entered the gas-flow heat exchanger through the action of the air supply fan, leaves the gas-flow heat exchanger and passes through an evaporator coil prior to entering a delivery conduit for delivery to the space being air-conditioned. Preferably the evaporator coil is selected from the group consisting of a chilled water coil, a vapor compression evaporator and a hot water coil. Preferably exhaust air having entered the gas-flow heat exchanger through action of the exhaust fan, leaves the gas-flow heat exchanger and passes through an evaporator pad where it is cooled by water to almost wet bulb temperature.
An air conditioning system utilizing a gas-flow heat exchanger in accordance with the first aspect of the invention as abovementioned, wherein a thermoelectric panel is placed in fluid communication with the lines containing outlet openings at the side of the stack, with a first portion of the thermo-electric panel in fluid communication with one of the lines containing outlet openings at the side of the stack associated with gas-flow paths of alternate pockets of the stack, and a second portion of the thermo-electric panel is in fluid communication with one of the lines containing outlet openings at the side of the stack associated with gas-flow paths of the remaining pockets of the stack, and a control module is disposed between the first and second portions of the thermo-electric panel. Preferably the thermoelectric panel comprises hot and cold finned heat sinks.
Preferably the application of a DC voltage to the control module induces a heating mode or a cooling mode to the air conditioning system depending on the polarity of the voltage.
An air conditioning system utilizing a gas-flow heat exchanger in accordance with the first aspect of the invention as abovementioned, wherein a water-jacket assembly is placed in fluid communication with the lines containing outlet openings at the side of the stack, with a first portion of the water jacket assembly comprising a first water coil fluidly connected to a first water jacket and a first pump and the first water coil adjacent with one of the lines containing outlet openings at the side of the stack associated with gas-flow paths of alternate pockets of the stack, and with a second portion of the water jacket assembly comprising a second water coil fluidly connected to a second water jacket and a second pump and the second water coil adjacent with one of the lines containing outlet openings at the side of the stack associated with gas-flow paths of the remaining pockets of the stack, and a control module is disposed between the first and second water jackets.
In an alternative arrangement, one of the first and second portions of the water jacket assembly is replaced by a set of air cooled fins adjacent to the control module.
A storage ventilator system for a cold room utilizing a gas-flow heat exchanger in accordance with the first aspect of invention as abovementioned, wherein fresh air entering the cold room passes through a first fan in fluid communication with one of the lines containing inlet openings at the side of the stack associated with gas-flow paths of alternate pockets of the stack, and exhaust air leaving the cold room passes through a second fan in fluid communication with one of the lines containing outlet openings at the side of the stack associated with gas-flow paths of the remaining pockets of the stack.
Preferably the first fan produces the same or slightly greater air volume across it as the second fan, thereby maintaining the air pressure within the cold room at substantially the same level or slightly greater as the outside air. Preferably the first and second fans are impeller fans.
In accordance with a second aspect, the present invention consists in a gas-flow heat exchanger comprising a set of parallel, spaced, heat-conductive areas providing between them a stack of pockets each containing parallel baffles which define a platen of passageways guiding the gas-flow path through the pocket between inlet and outlet openings, the openings being-arranged in four parallel lines at the sides of the stack, two of the lines respectively containing the inlet and outlet openings associated with the gas flow paths of alternative pockets of the stack, while the remaining two lines respectively containing the inlet and outlet openings associated with the remaining pockets of the stack of the heat exchanger, each pocket containing a removable frame formed with the openings provided at the ends of the gas flow path through it and supporting within the frame the parallel baffles which divide the gas-flow path into the platen of passageways, wherein the parallel heat-conductive areas separating the pockets from one another is formed from spaced rectangular or square areas of a sinuously wound heat conductive material characterized in that the heat conductive material is a moisture permeable material that can transfer both sensible heat and latent heat.
Preferably in one embodiment the moisture permeable material is paper. Preferably the paper has a high water strength texture. Preferably the paper is kraft paper. Preferably the kraft paper weighs about 45 grams per square meter.
Preferably in another embodiment the moisture permeable material is a finely woven plastic material.